Heathrow will not be able to expand to its promised 740,000 flights a year because of safety flaws involving its third runway, a new report claims.

The airport will be restricted to fewer than 700,000 flights annually, undermining a core pillar of its £17.6bn expansion plan, according to the report by the engineering consultancy Ebeni. The main concern is a new taxiway at the end of the northern runway, which it is claimed could interfere with departures.

Ebeni’s aviation experts think the tail fins of large aircraft such as the Airbus A380 superjumbo and Boeing 747 would infringe on the clearance space needed by other planes taking off.

This would mean the taxiway could be used only between departures, forcing the number of flights to…